(1) Field of the Invention
This invention relates generally to voltage-to-current converters and relates more particularly to voltage-to-current converters circuits having very low noise and low Gm transconductance for applications as e.g. integrator circuits required in sigma-delta modulators.
(2) Description of the Prior Art
Voltage-to-current converters are required if an input voltage from e.g. any measurement device has to be converted to a current to drive a device depending on the current injected into or sunk through its input. Such a device depending upon a current injected could be an integrating capacitor of a Gm integrator. Gm integrators are often employed in measuring technology e.g. in connection with sigma-delta modulators. In this context it is very important to achieve very low noise and low Gm transconductance together with a high linearity. For these linearity requirements it is necessary to use integration resistors with a Gm integrator.
It is a challenge for the designers of voltage-to-current converters used e.g. as Gm integrators in sigma-delta modulators to achieve low noise and low offset continuous time Gm integrators combining small integration resistors and high linearity, together with small chip size and a very low clock frequency
There are more known patents dealing with the design of integrator circuits.
(U.S. Pat. No. 7,002,501 to Gulati et al.) proposes a reconfigurable ADC including a plurality of reconfigurable blocks for allowing the ADC to provide a plurality of architectures. In one embodiment, the ADC can be configured to operate in a pipeline mode and a sigma-delta mode. This arrangement provides an ADC having a relatively large range of bandwidth and resolution.
(U.S. Pat. No. 5,227,795 to Yamakido et al.) discloses an over-sampling analog-to-digital converter using a current switching circuit as a local digital-to-analog converter, wherein a difference between the output currents of a voltage-to-current converter circuit and a current switching circuit is integrated by a capacitor of which the one end is grounded to a dc potential. Further, the current switching circuit has many bits to decrease the difference current between the signal current and the feedback current signal. Moreover, the level-shifting function of the voltage-to-current converter circuit makes it possible to apparently subtract the dc component from the input analog signal, which is produced based on an internally generated dc voltage as a dc bias voltage, and to decrease a change in the voltage between the electrodes of a capacitor caused by the integration of current.
U.S. Patent Application Publication (2005/0275575 to Motz) discloses an integrator circuit having an integrator unit performed to generate an integrated signal from a modulated input signal. Additionally, the integrator circuit has an error feedback coupler connected to an output of the integrator unit and to an input of the integrator unit and formed to determine an error component from the integrated signal or from a signal derived from the integrated signal and to compensate the error component via the feedback in the modulated input signal.